The present invention relates to a cationic thickener and a process for preparing the same, and more particularly to a cationic thickener which can be suitably used in, for instance, cosmetics, fragrant agents and the like, and a process for preparing the same.
Conventionally base gels have been investigated, and there have been known base gels comprising a salt prepared by neutralizing a crosslinked polyacrylic acid with an alkaline material as disclosed in Japanese Examined Patent Publication No. 4141/1957, Japanese Unexamined Patent Publication No. 46586/1976.
However, since those base gels have --COOH groups in their molecules, and their main structures are composed of anionic polymers prepared by neutralizing all or a part of the --COOH groups with NaOH, KOH, amine or the like, it is difficult to add raw materials for cosmetics for hair and scalp such as a cationic polymer for setting to the base gels. For instance, when a cationic polymer for setting having a quarternary amine in its molecule is added to the base gel, neutralization of electric charge occurs between the anionic polymer and the cationic polymer for setting, and thereby coagulation, cloudiness, turbidity and the like are sometimes caused.
Accordingly, polymers for setting which can be added to the anionic base gel (anionic polymer) are only nonionic polymers for setting such as polyvinylpyrrolidone and vinylpyrrolidone-vinyl acetate copolymer, and anionic polymers for setting represented by an alkanolamine solution of an acrylic resin.
Also, since an aqueous cosmetic composition containing the base gel forms a hard film after drying, when the aqueous cosmetic composition is used as, for instance, cosmetic composition for hair setting, peeling the film from hair, that is, flaking phenomenon occurs. Therefore, the use of the aqueous cosmetic composition has been limited.
On the other hand, as a base gel which forms a soft and flexible film after drying, there is known a base gel which is prepared by carrying out an aqueous emulsion polymerization of a crosslinkable base monomer having an amino group and then adjusting a pH value to increase its viscosity (Japanese Unexamined Patent Publication No. 133145/1982). However, since the crosslinkable base monomer is easily hydrolyzed, when the crosslinkable base monomer is hydrolyzed and then neutralized by an acid treatment, a cationic group is introduced into the crosslinkable base monomer. As a result, since an anionic group and a cationic group coexist in the same molecular chain of an obtained polymer, the polymer sometimes does not become uniform.
Also, when N,N-dimethylaminoethyl methacrylate is used as a raw material of the base gel described above, a desirable polymer cannot be obtained since hydrolysis is caused with violence during the polymerization reaction. In other words, this fact means that there cannot be used N,N-dimethylaminoethyl methacrylate which is widely and industrially used and known as a raw material for cosmetics having excellent properties, and that there is inconvenience in the selection of the starting monomer for the base gel. Also, there is a defect that the contamination with an impurity such as a surface active agent cannot be avoided in all of emulsion polymerizations.
U.S. Pat. No. 4,542,175 discloses a method of thickening an aqueous system containing an aqueous dispersion of a polymer comprising (A) 20 to 100% by weight of a basic unsaturated free radically polymerizable monomer having at least one basic nitrogen atom, (B) 0 to 95% by weight of a neutral unsaturated free radically polymerizable comonomer and 0 to 30% by weight of a neutral unsaturated free radically polymerizable comonomer, which is prepared by aqueous emulsion polymerization. However, a dialkylaminoalkyl (meth)acrylate having a short alkyl group like N,N-dimethylaminoethyl methacrylate cannot be used as one of the components for the polymer since the dialkylaminoalkyl (meth)acrylate is easily hydrolyzed during its polymerization reaction in water. Moreover, there are some defects such that impurities such as a surface active agent are contained in the resulting aqueous dispersion of the polymer, and that the polymer does not become uniform.
In order to solve the above problems, there is proposed a gel made of a copolymer prepared by copolymerizing a (meth)acrylic acid ester such as N,N-dimethylaminoethyl acrylate, an oxyalkylene di(meth)acrylate and a vinyl moonomer such as N-vinylpyrrolidone as disclosed in Japanese Unexamined Patent Publication No. 106114/1992. However, the gel is not good in flexibility and gloss of its formed film.
It is an object of the present invention to provide a cationic thickener which can be blended with a cationic polymer for setting.
It is a further object of the present invention to provide a cationic thickener which forms a flexible film after drying.
It is a still further object of the present invention to provide a cationic thickener containing little impurities.
It is a still further object of the present invention to provide a cationic thickener having excellent compatibility with a nonionic resin, a cationic resin and an amphoteric resin as well as water.
It is a still further object of the present invention to provide a cationic thickener having a high gel viscosity.
These and other objects of the present invention will become apparent from the description hereinafter.